You usually celebrate birthdays (to your friends and they also to you) with a koshinage for each year.

Haha...my dojo actually has a "tradition" where the birthday person gets thrown by everyone at the end of class. I already asked to get thrown on my birthday; one of my friends said I was "weird" to make that request.

"The ultimate aim of martial arts is not having to use them." - Miyamoto Musashi